1. Field of the Invention
The present invention relates to a sheet feeding apparatus which feeds a sheet, and an image forming apparatus including the sheet feeding apparatus.
2. Description of the Related Art
There has hitherto been known an image forming apparatus including a sheet feeding apparatus which automatically feeds sheets, stored in a sheet tray for storing sheets, one by one toward an image forming portion. The sheet feeding apparatus is provided with a feeding roller for feeding the uppermost sheet stored in the sheet tray, and a separation roller for separating sheets being multiply fed. By means of the feeding roller and the separation roller, the apparatus separates the sheets, stored in the sheet tray, one by one and feeds each separated sheet to the image forming portion.
For separation of the sheets, the separation roller is pressed against the feeding roller, while being applied via a torque limiter with rotational drive to rotate in a reverse direction to a feeding direction. Therefore, for example, when two or more sheets are fed by the feeding roller, since friction force between the sheets is smaller than friction force between the separation roller and the sheet, the separation roller rotates in the reverse direction to the feeding direction, to bring back second and subsequent sheets. On the other hand, when one sheet is fed by the feeding roller, rotational drive is blocked off by the torque limiter, and the separation roller rotates as driven by the feeding roller, to feed the sheet.
However, after the second and subsequent sheets have been brought back by the separation roller, the separation roller may be pulled by the first sheet and may thus repeat the aforementioned reverse rotation and driven rotation. When these rotational operations are repeated at a high speed, vibrations of the feeding roller and the like might be generated to cause generation of noise.
In order to deal with this, there has been proposed a sheet feeding apparatus in which a pressing member is pressed against a rotational shaft of the feeding roller to suppress vibrations so as to reduce generation of noise during feeding of sheets (refer to Japanese Patent Laid-Open No. 2003-160243).
Moreover, there has been proposed a configuration in which a sheet guide is movably provided in a projecting position where a sheet is guided between a feeding roller and a pair of conveying rollers and in a retreat position where feeding of sheets is not prevented (refer to Japanese Patent Laid-Open No. 2011-251807). According to this configuration, the sheet guide is moved to the projecting position when a sheet is pulled out by the conveying roller, thereby to switch a sheet conveying direction so as to reduce vibrations.
However, in the case of pressing the pressing member against the rotational shaft of the feeding roller to suppress vibrations, there is required a large-sized driving motor serving to increase a driving torque for driving the feeding roller so that an extra load is generated at the rotational shaft. Moreover, in the case of switching the sheet conveying direction at the time of pulling out the sheet to suppress vibrations, a switching mechanism for switching the conveying direction is required, which has been problematic.
Accordingly, it is desirable to provide a sheet feeding apparatus which, with a simple configuration, can suppress generation of noise during feeding of sheets without having an affect on sheet separating performance, and an image forming apparatus which includes this sheet feeding apparatus.